Spinning electrode fuel cell

ABSTRACT

A spinning electrode fuel cell is disclosed. The spinning electrode fuel cell includes a housing and a stacked disk assembly which is rotatably mounted in the housing. The stacked disk assembly includes multiple electrochemical cells connected to each other. A motor engages the stacked disk assembly for rotating the stacked disk assembly in the housing. A fuel flow pathway is provided in the housing for distributing a fuel to the electrochemical cells. An oxidant flow pathway is provided in the housing and physically separated from the fuel flow pathway for distributing an oxidant to the electrochemical cells. A method of fabricating a fuel cell is also disclosed.

FIELD OF THE INVENTION

The present invention relates to fuel cells. More particularly, thepresent invention relates to a spinning electrode fuel cell whichincludes rotating electrodes to reduce adverse effects of resistance togas diffusion while maintaining separation between the fuel andoxidizing agent in the fuel cell.

BACKGROUND OF THE INVENTION

Fuel cell technology potentially provides clean and efficient energy forstationary and traction applications. A functioning fuel cell, as anyother electrochemical device, requires a series of components thatprovide the key functions of reactant distribution (mass transport),catalytic reactivity, ionic separation, and current collection. To date,however, the efficiency of fuel cell systems remains well below itstheoretical maximum due to implementation practices that result insystem components that provide the means of delivering the key functionsbut concurrently increase the polarization of the cell (reduction involtage due to impedance of current) due to inefficiencies of design.

Recently, incremental improvements to fuel cell design havesubstantially reduced polarization contributed through componentproperties; for example, permeable membrane technologies have beendeveloped that provide thinner yet more robust membranes that are oflower resistance, catalyst alloys are being developed that reduce theloading necessary to achieve a given current density, and manufacturingtechniques that use stamped metal plates or innovativecarbon-manufacturing methods are used to improve the efficiency of thecurrent collection. Improvements to the reactant distribution, however,have focused on flow field design and pressurization of gases. Whilethese techniques sometimes improve the fuel/oxidant utilization, theycome at a cost of reduced efficiency (from increased fluid resistance)or increased complexity (from additional components that requireinstallation and their weight and cost).

A well-known means which is used to reduce the effects of mass transportin electrochemical systems is to use the “spinning disk” or “spinningband” technique, in which at least one of the electrodes is rotated athigh speed so that concentration gradients which are established due toresistance to mass transport (diffusion) are greatly reduced byhydrodynamically varying the rate at which electroactive species arebrought to the outer surface of the diffusion layer. These types ofelectrodes are typically used normally in liquid media for small singlecells. However, in the “spinning disk” type of fuel cell electrodearrangement, the fuel and the oxidizing agent are typically notseparately maintained.

Therefore, a spinning electrode fuel cell is needed in which theelectrodes of the fuel cell are rotated to reduce adverse effects ofresistance to gas diffusion and in which separation between the fuel andoxidizing agent in the fuel cell is maintained. Such a spinningelectrode fuel cell would extend the usefulness of the spinningelectrode arrangement to liquids and eliminate the predisposition of thesystem to extreme crossover currents, thus allowing the use ofconventional catalysts.

SUMMARY OF THE INVENTION

The present invention is generally directed to a spinning electrode fuelcell. The spinning electrode fuel cell includes a housing. A stackeddisk assembly is rotatably mounted in the housing and includes multipleelectrochemical cells connected to each other. A motor engages thestacked disk assembly for rotating the stacked disk assembly in thehousing. A fuel flow pathway is provided in the housing for distributinga fuel to the electrochemical cells. An oxidant flow pathway is providedin the housing and physically separated from the fuel flow pathway fordistributing an oxidant to the electrochemical cells. The invention isfurther directed to a method of fabricating a fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings, in which:

FIG. 1 is a perspective schematic view of an illustrative embodiment ofthe spinning electrode fuel cell according to the present invention; and

FIG. 2 is a sectional view of a stacked disk assembly of the spinningelectrode fuel cell according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring next to the drawings, an illustrative embodiment of a spinningelectrode fuel cell according to the present invention is generallyindicated by reference numeral 10 in FIG. 1. The spinning electrode fuelcell 10 typically includes a housing 12 which may be cylindrical, asshown, and contains a stacked disk assembly 14. A fuel inlet 16 isprovided at one end of the housing 12 for distributing a fuel 36containing hydrogen, for example, into the stacked disk assembly 14. Afuel outlet 32 is provided at the opposite end of the housing 12 fordistributing un-reacted fuel from the stacked disk assembly 14. Anoxidant inlet (not shown) and an exhaust outlet (not shown) are furtherprovided in the housing 12 for distributing an oxidant 38 containingoxygen into the housing 12 and distributing excess oxidant 38 withexhaust water from the housing 12, respectively.

As shown in FIG. 2, the stacked disk assembly 14 includes multipleelectrochemical cells 18 which may be generally disk-shaped and areelectrically connected to each other in series to form a stackedconfiguration. Each electrochemical cell 18 includes a reservoir plate20 which acts as a physical barrier between a fuel gas flow pathway 17and an oxidant flow pathway 34 on the interior and exterior,respectively, of the stacked disk assembly 14. At respective ends of thestacked disk assembly 14, the fuel flow pathway 17 is provided in fluidcommunication with the fuel inlet 16 and the fuel outlet 32.Furthermore, the oxidant flow pathway 34 is provided in fluidcommunication with the oxidant inlet (not shown) and exhaust outlet (notshown) which may be at respective ends of the stacked disk assembly 14.

Each electrochemical cell 18 further includes a membrane electrodeassembly (MEA) 22 which is attached to the reservoir plate 20. The fuelflow pathway 17 typically extends between the reservoir plate 20 and theMEA 22 of each electrochemical cell 18. The oxidant flow pathway 34typically extends between the MEA 22 of each electrochemical cell 18 andthe reservoir plate 20 of the adjacent electrochemical cell 18. The MEA22 typically includes a porous support plate (not shown) to which isattached a proton permeable membrane 24 that is sandwiched between apositive (anode) catalyst layer 26 and a negative (cathode) catalystlayer 28. Preferably, the positive catalyst layer 26 is exposed to thefuel flow pathway 17, whereas the negative catalyst layer 28 is exposedto the oxidant flow pathway 34. Radial insulators 30 contact either theanodic current collector (for the negative electrode) or the cathodiccurrent collector (for the positive electrode) and also provide a sealbetween the fuel flow pathway 17 and the oxidant flow pathway 34. TheMEA assembly 22 is multi-functional, providing a mechanical foundation,a bipolar collection medium, an ion transport mechanism and a catalystfor both the anode and the cathode of each electrochemical cell 18.Throughout the length of the stacked disk assembly 14, the MEA 22 ofeach electrochemical cell 18 is connected to the reservoir plate 20 ofthe adjacent electrochemical cell 18 in the series.

It will be understood that the positions of the fuel flow pathway 17 andthe oxidant flow pathway 34 in and around, respectively, the stackeddisk assembly 14 may be reversed such that the fuel flow pathway 17 isoutside and the oxidant flow pathway 34 is inside the stacked diskassembly 14. In that case, the positions of the positive catalyst layer26 and the negative catalyst layer 28 would be reversed with respect totheir respective positions shown in FIG. 2. Furthermore, the fuel inlet16 shown in FIG. 1 would become the oxidant inlet for distribution ofthe oxidant into the housing 12.

The support plate (not shown) of each MEA 22 may be a carbon or coatedmetal plate which is designed to meet the requirements of optimummechanical strength and electrical conductivity. The support plate mayalso be manufactured with appropriate indentations and patterns toincrease turbulence and reduce barrier layers. The MEA 22 may be formedas a sandwich construction in which the support plate, positive catalystlayer 26, membrane 24 and negative catalyst layer 28 are arranged andpressed together. Alternatively, the MEA. 22 may be formed as a seriesof catalysts and components which are sequentially cast or painted ontothe support plate, as is known to those skilled in the art.

The stacked disk assembly 14 is mounted for rotation inside the housing12 according to the knowledge of those skilled in the art. A motor 15engages the stacked disk assembly 14 for rotation of the stacked diskassembly 14 in the housing 12. The MEAs 22 and the reservoir plates 20of the electrochemical cells 18 are radially concentric, such that theentire stacked disk assembly 14 can be rotated inside the housing 12 ata high angular speed ω. Due to the current-collecting configuration ofthe stacked disk assembly 14, one end of the stacked disk assembly 14 ispositively-charged whereas the opposite end of the stacked disk assembly14 is negatively-charged, as shown in FIG. 2. Electrical current may beremoved from the rotating stacked disk assembly 14 using brushes (notshown) or other conventional means known to those skilled in the art.

In FIGS. 1 and 2, each of the MEA/support plate assemblies 22 is shownas a plate. However, it will be appreciated by those skilled in the artthat the MEA/support plate assemblies 22 may alternatively be formed inthe configuration of an annular ring (not shown), in which case eachMEA/support plate assembly 22 has a reduced active surface area and auniform velocity field.

In operation of the spinning electrode fuel cell 10, the motor 15rotates the stacked disk assembly 14, as indicated by the arrow in FIG.2. A fuel 36, which may be a gas or liquid containing hydrogen, forexample, is distributed into the fuel flow pathway 17 through the fuelinlet 16 of the spinning electrode fuel cell 10. Simultaneously, anoxidant 38 (FIG. 2), which may be a gas or liquid containing oxygen, forexample, is distributed into the oxidant gas flow pathway 34 fromoutside the housing 12. In the fuel flow pathway 17, the fuel 36contacts the positive catalyst layer 26 of each MEA 22. Accordingly,electrons are harvested from the fuel 36 as the fuel 36 is oxidized. Theharvested electrons are distributed through an external circuit (notshown), such as an electric drive motor (not shown) of a fuel cellvehicle, for example. The protons pass through the membrane 24 to thenegative catalyst layer 28 of the MEA 22. At the negative catalyst layer28, electrons returning from the external circuit combine with theprotons from the membrane 24 and oxygen in the oxidant 38 to form wateras a by-product. The exhaust water is distributed from the oxidant flowpathway 34 and discharged from the housing 12 through the exhaust outlet(not shown) provided in the housing 12.

The stacked disk assembly 14 may be oriented in a vertical orientation,as shown, or in a horizontal orientation (not shown) for optimum spaceutilization; however, a horizontal orientation would provide advantagesof simplified immobilization of the fuel if a liquid fuel were used.Delivery of the fuel 36 or the oxidant 38 throughout the stacked diskassembly 14 may be enhanced with appropriate fins (not shown) providedon the rotating stacked disk assembly 14 in order to reduce or eliminatethe need for a secondary fluid handling system. A liquid seal (notshown), combined with a float valve (not shown) for the introduction ofgas, may be used to maintain fuel pressure within the stacked diskassembly 14 as well as to separate the fuel 36 from the oxidant 38.

It will be appreciated by those skilled in the art that the spinningelectrode fuel cell 10 according to the present invention has a numberof advantages. For example, transport of the fuel and oxidant isconducted at high cross-section/low velocity as compared to aconventional restricted flow field, thereby reducing pressure drop andgas pumping inefficiencies. Furthermore, the active materials aresupplied in a nearly parallel manner, minimizing catalyst utilizationproblems where fuel and oxidant gradients lead to preferentialdegradation near the inlet or the outlet of the fuel cell. The angularvelocity of the stacked disk assembly is adjustable to optimize powerrequirements (faster rotation favors higher currents), but this notnecessary. This facilitates an advantage in the ability to provide rapidtransient response. Oxidative by-product management is improved throughthe centrifugal action of the rotating stacked disk assembly 14. Forexample, liquid water would be driven from the MEAs under rotatingaction, eliminating common problems associated with liquid waterbuild-up such as catalytic site and gas channel blockage. The findesign, coupled with a minimization of the gas diffusion layer andmembrane resistance, allows efficient low-pressure drop cooling of theMEA, thus eliminating the need for a dedicated heat-exchange system. Thefuel cell is inherently manufacturable, using largely stamped parts andcrimped welds, both of which are well-known in the art. The fuel cell iscompatible with both gaseous and liquid media.

While the preferred embodiments of the invention have been describedabove, it will be recognized and understood that various modificationscan be made in the invention and the appended claims are intended tocover all such modifications which may fall within the spirit and scopeof the invention.

1. A fuel cell comprising: a housing; a stacked disk assembly rotatablymounted in said housing and comprising a plurality of electrochemicalcells connected to each other; a motor engaging said stacked diskassembly for rotating said stacked disk assembly in said housing; a fuelflow pathway provided in said housing for distributing a fuel to saidplurality of electrochemical cells; and an oxidant flow pathway providedin said housing and physically separated from said fuel flow pathway fordistributing an oxidant to said plurality of electrochemical cells. 2.The fuel cell of claim 1 wherein each of said plurality ofelectrochemical cells comprises a reservoir plate and a membraneelectrode assembly carried by said reservoir plate.
 3. The fuel cell ofclaim 2 further comprising at least one radial insulator engaging saidreservoir plate and said membrane electrode assembly.
 4. The fuel cellof claim 3 wherein said at least one radial insulator comprises a pairof radial insulators.
 5. The fuel cell of claim 2 wherein said membraneelectrode assembly comprises a positive catalyst layer, a negativecatalyst layer and a proton permeable membrane sandwiched between saidpositive catalyst layer and said negative catalyst layer.
 6. The fuelcell of claim 5 wherein said positive catalyst layer is exposed to saidfuel flow pathway and said negative catalyst layer is exposed to saidoxidant flow pathway.
 7. The fuel cell of claim 5 wherein said positivecatalyst layer and said negative catalyst layer are painted on saidmembrane.
 8. The fuel cell of claim 5 wherein said positive catalystlayer, said membrane and said negative catalyst layer are compressedtogether.
 9. A fuel cell comprising: a housing; a stacked disk assemblyrotatably mounted in said housing and comprising a plurality ofelectrochemical cells connected to each other; a motor engaging saidstacked disk assembly for rotating said stacked disk assembly in saidhousing; a fuel flow pathway provided in said stacked disk assembly fordistributing a fuel to said plurality of electrochemical cells; and anoxidant flow pathway provided outside said stacked disk assembly andphysically separated from said fuel flow pathway for distributing anoxidant to said plurality of electrochemical cells.
 10. The fuel cell ofclaim 9 wherein each of said plurality of electrochemical cellscomprises a radially-extending reservoir plate and a radially-extendingmembrane electrode assembly carried by said reservoir plate.
 11. Thefuel cell of claim 10 further comprising a plurality of radialinsulators engaging said reservoir plate and said membrane electrodeassembly.
 12. The fuel cell of claim 10 wherein said membrane electrodeassembly comprises a positive catalyst layer, a negative catalyst layerand a proton permeable membrane sandwiched between said positivecatalyst layer and said negative catalyst layer.
 13. The fuel cell ofclaim 10 wherein said reservoir plate of each of said electrochemicalcells engages said membrane electrode assembly of an adjacent one ofsaid electrochemical cells.
 14. The fuel cell of claim 13 wherein saidfuel flow pathway extends between said reservoir plate and said membraneelectrode assembly of each of said electrochemical cells and saidoxidant flow pathway extends between said membrane electrode assembly ofeach of said electrochemical cells and said reservoir plate of anadjacent one of said electrochemical cells.
 15. The fuel cell of claim14 wherein said membrane electrode assembly comprises a positivecatalyst layer exposed to said fuel flow pathway, a negative catalystlayer exposed to said oxidant flow pathway and a proton permeablemembrane sandwiched between said positive catalyst layer and saidnegative catalyst layer.
 16. A method of fabricating a fuel cell,comprising: providing a housing; forming a stacked disk assembly byproviding a plurality of electrochemical cells and connecting saidplurality of electrochemical cells to each other; rotatably mountingsaid stacked disk assembly in said housing; connecting a motor to saidstacked disk assembly for rotating said stacked disk assembly in saidhousing; providing a fuel flow pathway in said housing in fluidcommunication with said plurality of electrochemical cells; andproviding an oxidant flow pathway in said housing in physical separationwith respect to said fuel flow pathway.
 17. The method of claim 16wherein said providing a plurality of electrochemical cells comprisesproviding a radially-extending reservoir plate, providing aradially-extending membrane electrode assembly and attaching saidradially-extending membrane electrode assembly to said reservoir plate.18. The method of claim 17 further comprising providing a plurality ofradial insulators engaging said reservoir plate and said membraneelectrode assembly.
 19. The method of claim 17 wherein said providing aradially-extending membrane electrode assembly comprises providing asupport plate, a positive catalyst layer, a membrane and a negativecatalyst layer and pressing said support plate, said positive catalystlayer, said membrane and said negative catalyst layer together.
 20. Themethod of claim 17 wherein said providing a radially-extending membraneelectrode assembly comprises providing a support plate, painting apositive catalyst layer on said support plate, painting a membrane onsaid positive catalyst layer and painting a negative catalyst layer onsaid membrane.